Zinc Oxide Nanostructures for Flexible and Transparent Electronics

As a multifunctional material, ZnO possesses remarkable and unique properties and has attracted much research interest for use in a variety of applications. Especially, it has been regarded as a leading material for flexible and transparent electronics, which is a promising emerging technology in electronics. This dissertation studies doping behavior of Ga in ZnO for transparent electrode applications and presents new approaches to ZnO nanostructures for next-generation flexible and transparent electronics. These approaches include developing techniques that enable multiple stacked ZnO nanoflowers and thermal treatment processes at high temperature. Transparent conductive oxides have been extensively studied for the use as a transparent electrode, which is one of the most fundamental and essential parts in transparent electronic devices. In this study, Ga-doped ZnO nanorods were grown on glass substrates, and the effects of Ga doping concentration on the physical properties of ZnO nanorods were investigated using various characterization tools. ZnO nanoflower is a highly preferred nanostructure for solar cells, sensors, and photodetectors due to its high surface area to volume ratio. To-date, ZnO nanoflowers have mostly been synthesized in the form of nanopowders without a substrate, and ZnO nanoflowers grown on substrates have only been single-stacks. Atmospheric pressure plasma jet treatment was used to increase the surface area to volume ratio of ZnO nanoflowers. The plasma treatment induced a significant increase in the height and density of the ZnO nanoflowers/nanorods because the plasma effectively increased the surface energy and roughness of the seed layers while barely affecting the crystal shape and phase of the ZnO nanoflowers/nanorods. Flexible and transparent mica substrates were used for the growth of vertically well-aligned ZnO nanorods. The adoption of mica as a substrate material permitted high temperature annealing processes, which improved the structural and optical properties of ZnO nanorods with uniform surface coverage and excellent adhesion. A practical application for the synthesized ZnO nanorods is also presented in this dissertation. ZnO nanorod-based flexible and transparent dye-sensitized solar cells (DSSCs) and piezoelectric nanogenerators (NGs) were fabricated and the device performances were investigated. Although only two kinds of energy-harvesting devices (DSSCs and NGs) are presented as examples of applications in this dissertation, it is expected that this new approach will provide a breakthrough for overcoming the limited process temperature on plastic and cellulose nanopaper substrates because mica can be extensively used as a flexible and transparent substrate material for electronics, optoelectronics, energy/environmental, and biomedical applications where high temperature processes are required

Graphene-Based Interconnects for Stable Dye-Sensitized Solar Modules

We present Z-Type Dye Sensitized Solar Modules (DSSMs) with screen printed graphene-based vertical interconnects. This prevents corrosion of interconnects in contact with electrolytic species, unlike conventional Ag interconnects. By enlarging the width of single cells, or by increasing the number of cells, we get an enhancement of the aperture power conversion efficiency similar to+12% with respect to Ag-based modules, with 1000 h stability under 85 degrees C stress test. This paves the way to original design layouts with decreased dead area and increased generated power per aperture area

Optimizing a Simple Natural Dye Production Method for Dye-Sensitized Solar Cells: Examples for Betalain (Bougainvillea and Beetroot Extracts) and Anthocyanin Dyes

We present a study about the sensitizers extracted from natural resources. This paper focuses on how to select, extract and characterize natural dyes, giving some guides to establish a protocol for the whole process of fabricating and using these dyes. The influence of the extraction solvent and method, and of parameters such as pH are analyzed. Also, dye precursor and dye extract stability have been studied, as well as how the dye adsorbs onto substrates and the effect of mixing or concentrating the extracts. Results concerning betalain pigments present in bougainvillea and beetroot extracts, and anthocyanins in eggplant extracts, analyzed by using UV-Vis spectrometry, are included. As an example of application, we report procedures intended to test and enhance the dye potential as a main component of dye-sensitized solar cells (DSSCs). DSSCs mimic nature’s photosynthesis and have some advantages like an easy and low-cost fabrication procedure. Their efficiency depends on its design and fabrication process and also on the different components involved. Hence, optimizing each component is essential to achieve the best performance, and thus the dye used as a sensitizer is crucial. We fabricate cells by using a simple procedure: As the interest is focused on the sensitizer, the same consecutive steps are followed, varying only the dye extract. Among all the natural-dyes tested, beetroot extract reaches up to 0.47% cell efficiency, which is near the highest values found in literature for this pigment

Effects of Structure and Morphology of Hydrothermally Grown ZnO Particles on the Photovoltaic Performance of Dye Sensitized Solar Cell

Highly ordered microporous ZnO materials with crystalline structure were synthesized hydrothermally from three different Zn-precursorsnamely: Zinc-acetate, chloride, and nitrate. XRD investigations revealed that all the obtained powders have single phase zincite structure. The powder morphology was investigated by SEM which showed that the starting Zn-precursor affects the shape as well as the size of the obtained particles. A photoelectrodes fabricated using the three different synthesized microporous ZnO particles showed variation in photocurrent density (Jsc) dye loading and hence the efficiency with variation in structure texture, morphology and particle size. DSSC built with photoelectrodes made from Zn-acetate has the highest efficiency (5.4%) which is attributed to having lowest particle size and largest surface area available for dye loading. This increases light harvesting at the photoelectrode which in turn increases short circuit current density. On the other hand, the lowest current density (5.65mA/cm2) is obtained for DSSC with photolelctrodes made from Zn-nitrate

Optimizing room temperature binder free TiO2 paste for high efficiency flexible polymer dye sensitized solar cells

Binder free TiO2 paste is prepared using tert-butyl alcohol in dilute acidic conditions at room temperature for flexible polymer dye sensitized solar cells (DSSCs). The present paper reports the detailed studies carried out to elucidate the importance of stirring times during the paste preparation on the final device performance. The maximum conversion efficiency of 4.2% was obtained for flexible DSSCs fabricated on tin doped indium oxide/polyethylene naphthalate substrates using TiO2 paste prepared with an optimum stirring time of 8 h. The effect of optimum stirring times on the device characteristics has been understood in terms of the detailed morphology and surface area measurements

Solar Cells

The second book of the four-volume edition of "Solar cells" is devoted to dye-sensitized solar cells (DSSCs), which are considered to be extremely promising because they are made of low-cost materials with simple inexpensive manufacturing procedures and can be engineered into flexible sheets. DSSCs are emerged as a truly new class of energy conversion devices, which are representatives of the third generation solar technology. Mechanism of conversion of solar energy into electricity in these devices is quite peculiar. The achieved energy conversion efficiency in DSSCs is low, however, it has improved quickly in the last years. It is believed that DSSCs are still at the start of their development stage and will take a worthy place in the large-scale production for the future